Power transmission



Sept. 7, 1943. K. R. HERMAN ET AL 955 2 POWER TRANSMISSION Filed June 16, 1942 a INVENTOR KENNETH R. HERMAN 8" BY FERRIS T. HA RINGTON WZ/M ATTORNEY otherwise likely to occur.

Patented Sept. 7, 1943 POWER TRANSMISSION Kenneth R Herman, Franklin, and Ferris T. Harrington, Detroit, Mich., assignors to Vickers Incorporated, Detroit, Mich., a corporation of Michigan Application May'16, 1942, SeriafNo. 443,219 2 Claims. (01. 121-45) This invention relates to power transmissions, particularly to those of the type comprising two or more fluid pressure energy translating devices, one of which may function as a pump and an- Transmissions of this character are widely used on machine tools for actuating reciprocating slides, rotary spindles, etc. It is frequently necessary in applications of this character to make provision for sudden and wide fluctuations in motor load, as, for example, when a cutting tool breaks through a work piece, and to so arrange the circuit that the motor is positively prevented from ever jumping ahead under'a sudden reliefin load.

There are in use several methods which accomplish this result, one method comprising the use of a back-pressure valve in the motor outlet line which acts to maintain a predetermined back pressure therein. Systems of this character present one drawback particularly troublesome in large size machines, namely, that the back-pressure valve is an energy dissipator, and, if the back pressure which must be maintained is very highand the volume of fluid passed therethrough is also high, a considerable heating of the oil occurs which adversely affects the system as a whole. In addition, the waste of power at the backpressure valve requires [a larger power input to: the machine and thus gives the circuit as a whole a low efficiency.

It is an object of the present invention to provide an improved power transmission system wherein the above difiiculties are avoided,,at least to a substantial extent, and at the same time to positively prevent any jumping ahead of the fluid motor under a sudden relief in load.

A further objectis to provide a' system of this character wherein a relatively low value of back pressure is normally maintained in the motor outlet when the motor load is sufficiently high to, of itself, prevent jumping ahead. At thesame time,additional means are provided for increasing the back pressure to a higher value whenever the motor load falls below a certain value. In this way it is assured that the'high back pressure valve shown in Figure 1.

Inthe drawing:

Fi re '1 is a diagrammatic view of a power trangr nission system embodying a preferred form of the present invention.

Fl ure 2 is an enlarged view of a portion of 9.

There is indicated at ID a pump adapted to be driven by a suitable prime mover, such as an electric motor 12. The pump l0 withdraws fluid from a tank l4 through a suction conduit l6 and delivers the same to a delivery conduit l8. The latter has a relief valve 20 of conventional construction for bypassing oil to the tank l4 through a conduit 22 whenever a predetermined pressure is exceeded in the delivery conduit l8.

The conduit, l8 extends to a direc'tional fourway valve 24 which directs the flow of liquid from the pumplll to and from either end of the cylinder-54. The directional valve 24 comprises a main body member having a longitudinal bore 26 within which is mounted a siidable spool 46. The bore 26 is provided with a plurality of annular ports arranged along its length, of which 28 is the pressure port, 30 and 32-the cylinder ports, and 40 and 42 the tank ports. The pressure port communicates with the delivery conduit l8, while the tank ports 40 and 42 communicate with the tank l4 through aconduit 44.- The cylinder ports 4 30 and 32 communicate with motor connections necessary to prevent jumping ahead is applied only during intervals when jumping ahead is 36 and 38, respectively, which lead to the opposite ends of a fluid-motor 54. The lattercomprises a cylinder within which is mounted a reciprocable piston 66 to move a rod 58 and cause it to do work.

The spool 46 of valve 24 is provided with solid lands 50 and-52 which close the cylinder ports 30 and 32 whenthe spool is incentral position, illustrated. The righthand end of the spool 46 has secured thereto an operating stem 43 which is attached to a manually operated lever 48.

Conduit 36 extendsfrom port 30 of valve 24 to the head end of cylinder 54 through a hydrostatic flow control valve which controls the rate of liquid flow theretou Valve 60 includes an adjustable throttle valve 62 which limits the rate of fluid flow and a pressure compensator 64 which maintains the rate of controlled flow independent of the variations in the operating pressure or fluctuations in cutting tool resistance. The pressure compensator 64 consists of a piston 66, a piston spring 68 and a valve Ill. Piston 66 is mounted in a cylinder 12 from which two passages .14 and 16 extend, one from each side of piston 66 to the opposite sides of the throttle 62. A

light spring 63 tends to keep open valve 64 by r urging it to the left. The hydrostatic pressure compensator 64 regulates the fluid flow to the throttle 62 in accordance with the pressure drop across the throttle 62, that is, as pressure in port I8 rises slightly, the piston 66 will move to the right, pressure on its left side being greater than that on its right, and continue to close valve I until the rate of liquidfiowing into port i8 is the same as that of the liquid being discharged through the throttle 62. Since the rate of discharge through the throttle 62 will remain constant, the rate of movement of the working tool will also be relatively constant. The flow control valve 60 contains an integral check valve 82 to allow free flow in the Opposite direction. A drain conduit 92 connects to the throttle valve 62 at a point below the plane of the drawing for the purpose of collecting seepage lengthwise of the throttle valve stem.

Attached to the exhaust end of the cylinder 54 by a conduit 38 is a valve 84 for providing back pressure therein to firmly hold the piston 56 as it moves through its work stroke. Valve 84 comprises a main body having a central longitudinal bore 85 which is provided with ports I00 and IN, communication between which is controlled by a movable spool 86. The latter has two lands 81 and 89 which are freely slidable with a close fit in bore 85 and also a projection 9| on its left end.

The body- 84 includes two means for actuating the valve spool 86, one of which consists of an auxiliary passage 93 extending from port I00 to orifice 95 which connects with chamber I03 in which a slidable plunger 90 is mounted for moving the valve spool 86 by a fluid pressure exerted on the left end of the plunger 90 in opposition to the force of the spring 94. The other said means consists of an orifice 98 which extends from the left end'of the bore 85 to the side of the main body Where it connects with a conduit 88 which is in communication with the inlet conduit 36. The main body contains also a check valve 98 to provide for the reverse flow.

On the righthand end of the main body is secured an end cap I through which is threaded an adjusting screw 96. A spring 98 extends from within the screv. 96 to the valve spool 86 holding it in a closed position to the left, disconnecting the ports I00 and NH. The spring 96 is adjusted by the screw 96 to whatever back pressure in cylinder 54 is desired. vA chamber I if in the end cap I05 is in communication with the end of the bore 85 for exhausting oil from the core. 85 through passage 1 I3 which is externally connected to a conduit 92 permitting free flow to the tank I4. The end cap I05 also carries a lock nut H5 back piston 56 at a certain rate of speed as determined by adjustment of the throttle valve 62. The metered liquid also enters conduit 88 leading to valve 84, exerting equal pressure in either conduit.

The discharging liquid from the back of piston 56 enters the foot valve 84 through conduit 38 and encounters a resistance at port I00 before flowing through it to port IN. The resistance to discharge of back pressure on the discharge end of the cylinder helps prevent surging of the piston 56 after the work is completed and also maintains back pressure proportional to the load fluctuations, thus preventing jerky action on the feed stroke.

This resistance may be overcome either by a direct action, that is, whenever pressure in port I00 rises above the value for which the spring 94 is set, valve spool 86 will move to the right perand a closure cap 1, both secured on the screw In operation, While pump I0 is being driven by the electric motor I2, oil is withdrawn from the tank I4 through a suction conduit I6 and delivered through conduit to the directional valve 26. With the spool 46 in neutral position, illustrated, the full pump delivery is bypassed to the tank 14 through a relief valve 20 via conduits 22 and 48.

To advance the'piston 56, lever 48 of valve 24 is pushed inward. This allows the pump delivery to be directed from the pressure port 28 to motor port 30 where it is delivered by conduit 36 to the flow control valve 60. The fluid flow enters valve mitting oil to be bypassed from port I00 to port IOI until the pressure in port I00 drops below the setting of spring 94, or by a remote action, that is, by pressure supplied by conduit 88 acting over the left end of spool 86. By this arrange ment it will be seen that pressure in either port 99 or I00 will at times aid the other in the shifting of the spool 86.

Although a predetermined pressure for which the valve spring 94 has been adjusted must be reached to cause the spool 86 to open and allow liquid to flow through port I00 to port IOI to tank, pressure required to hift spool 86' will be less in port 99 than in port I 00. This is caused by the difference in areas over which the pressure acts. Pressure from conduit 88 acts over the entire left end of spool 86 which is greater in area than is the left end of plunger 90. Thus, it will be seen that valve 84 may be made to operate either at low pressure, remotely, or at high pressure, directly. 4

During the feed-in operation with zero load to overcome, before the piston 56 can be forced back, because of the resistance encountered by the liquid at valve 84, a certain pressure must be built up in front of the piston 56. Because of the I sufiicient to open the spool 86, but the combined lifting force of both will produce the desired effect, allowing the discharged liquid to flow to the tank, with port 98 supplying the greater lifting force.

As the load on the rod 58 increases, pressure will increase in the inlet conduit 36 which will I be transmitted to port 99 causing the-spool 86 to be moved more to the right, allowing a greater volume of liquid to be discharged, thus lessening the back pressure. As the spool 86 is moved to the right,the aiding force of the plunger 90 is 60 at port 18, flows by valve I0 of pressure compensator 64 to the throttle 52 where it is metered into the inlet line 36 of cylinder 54, and forces lessened proportionately, for the pressure in port port 32 providing for rapid return.

If, however, the load drops to zero, the valve begins to operate at high pressure directly, acting in the capacity of a relief valve, by-passing oil until sufiicient pressure is again built up in port 99. It is at this phase that the plunger 90 is dominant in lifting the spool 8'6.

To reverse the operation, returning the piston 55 to its former position, lever 48 is pulled outward. This connects pressure port 28 with motor The full pump delivery is now directed to conduit 38, to port "ll of valve 84, unseating' the check valve 88, flowing around valve spool 86, through port I to the rod end of the cylinder 54. Liquid discharging from the front of the piston 56 will be by-passed around flow control valve 60 through conduit I04, unseating the check valve 82, to port 18 where it is delivered to valve 24 by conduit 36. The valve spool 46, being in the extreme right position, will'direct the liquid to tank conduit 44 leading totank l4.

Thus it will be seen that the present invention maintains back pressure while "feeding-in and at the same time keeps the oil in the circuit much cooler than heretofore because during normal load conditions the motor exhaust fluid flow passes to the tank freely through the back-pressure valve. At the same time, any jumping ahead of the slide as upon sudden falling off of load resistance is prevented.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In a hydraulic power transmission system the combination with a source of pressure fluid, a fluid motor operable by fluid supplied from said source, supply and return conduits connecting the source with the motor, a flow controller in the supply line for regulating the rate of flow to the motor, and a back pressure valve in the return conduit responsive both to motor outlet pressure to produce a variable but limited amount I of, back pressure in the return conduit and also to motor inlet pressure to maintain the sum of the pressures produced in the supply conduit by said back pressure and by motor load above a predetermined minimum, said valve having a small operating piston exposed to motor outlet pressure and a larger operating piston exposed to motor inlet pressure and resilient means opposing the pressures efiective on said means.

2. In a hydraulic power transmission system the combination with a source of pressurefluid, a fluid motor operable by fluid supplied from said source, supply and return conduits connecting the'source with the motor, a flow controller in the supply line for regulating the rate of flow to the motor, a back pressure valve in the return conduit responsive both to motor outlet pressure to produce a variable but limited amount of back pressure in the return conduit and also to motor inlet pressure to maintain the sum of the pressures produced in the supply conduit by said back pressure and by motor load above a predetermined minimum, said valve having a small operating piston exposed to motor outlet pressure and a larger operating piston exposed to motor inlet pressure and resilient means opposing the pressures eifective on said means, and a single adjusting means for varying the force of said resilient means whereby both the predetermined low back pressure and the predetermined minimum inlet pressure may be simultaneously adjusted.

KENNETH R. HERMAN. FERRIS T. HARRINGTON, 

